In recent years, mechanical drive systems in vehicles have been gradually replaced by electrical drive-by-wire systems, in which components are driven by electric motors to improve space efficiency, assemblability, controllability, and the like. One example of such replacement may be found in a transmission shift position switching mechanisms. In such a system, when a target shift position is changed according to an operation of a shift control lever or the like, the shift position is controlled to be in the target shift position by rotating the motor to a target rotation position corresponding to the target shift position.
A shift position switching controller disclosed in a patent document 1 (i.e., Japanese Patent Application No.: JP 2008-2561 A) provides a pre-fetch control that pre-starts the switching of the shift position to an N position in order to reduce a shift position switch time, when the shift control lever passes an N lever position during the shift position switching, that is, at a moment of detecting that the shift control lever is in the N lever position without knowing which lever position is the target lever position.
The applicant of the present disclosure is now studying a shift position switching system that prevents a mis-shift to the N position, that is, a non-intended shift position switching to the N position. The shift position switching system is configured to perform a switching of the target shift position to the N position only when a request position signal is switched to an N position signal and continue to be an N position signal at least for a preset time, that is, at least after an N position check time.
In such a system, as shown in FIG. 4B, by reducing the N position check time, a required time between (i) the switching of the request position signal to the N position signal and (ii) the switching of the target shift position to the N position is reduced. In such manner, a switch time between (i) the switching of the request position signal to the N position signal and (ii) the rotation of the motor to the rotation position that corresponds to the N position (i.e., an actual switching of the shift position to the N position) is reduced in comparison to a conventional switch time that includes a not-reduced N position check time (cf. FIG. 4A).
However, by reducing the N position check time, the switch time may be extended in some cases. For example, as shown in FIG. 5A/B, such a reverse effect may be observed when the request position signal is switched to the R position signal immediately after (i.e., subsequent to) the switching to the N position signal. In such a case, as shown in FIG. 5B, soon after the switching of the request position signal to the N position signal, the target shift position is switched to the N position, and a rotation drive control of driving the motor to the “N shift rotation position” (i.e., abbreviated to “N shift” hereafter, representing a motor rotation position corresponding to the N position) is started, due to the reducing of the N position check time. Then, due to a further switching of the request position signal to the R position signal, the rotation drive control is switched to rotate the motor to the “R shift rotation position” (i.e., abbreviated to “R shift” hereafter, representing a rotation position corresponding to the R position). That is, the rotation drive control of the motor is switched, from the driving of the motor to the N shift to the driving of the motor to the R shift during the driving of the motor to the N shift, which causes an “overshoot” rotation, that is, the rotation position of the motor returns to the R shift after passing the R shift first to approach the N shift. Therefore, the switch time between (i) the switching of the request position signal to the N position signal and (ii) the driving of the motor to the N shift, i.e., to the rotation position corresponding to the N position (i.e., an actual switching of the shift position to the N position) is extended in comparison to a conventional switch time that includes a no-reduced the N position check time (see FIG. 5A). That is, responsiveness of the switching of the shift position to the R position is deteriorated.